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What Causes Curly Cannabis Leaves And How To Cure Them

There are numerous reasons why you might find curly cannabis leaves in your grow-op. This guide will explain why this phenomenon occurs, and what you can do to prevent it from ruining your final product.

Contents:

Cannabis plants can’t vocalise a call for help—but they can send signals to tell you all is not well. If you see leaves either clawing or curling, there is trouble with the trees. Don’t ignore their pleas. This blog will help you identify the causes and cures for curly cannabis leaves.

CAUSE: OVERWATERING

Overwatering will literally drown your plant’s roots. Excess water will not only rinse most of the beneficial microbes from the medium, a sodden substrate can also become colonised by algae and nasty fungi. Persistent overwatering invariably invites the parasitic Pythium, better known as root rot. Cannabis plants with droopy, claw-like leaves could be trying to tell you they are waterlogged.

“Water mould” microorganisms are just like vampires; you have to invite them in before they can do any harm. Keep them out of the garden by making sure they are not welcome. Maintaining an effective wet-dry cycle is all it takes. If you can pick up your pots, do it. Then you can tell by their weight when it’s time to water.

If you can’t lift the containers, then consider a moisture meter and make sure to carefully monitor post-watering plant behaviour. Try reducing the volume of water. Alternatively, take longer intervals between waterings. Unfortunately, Pythium is virtually incurable and will turn your plant’s roots into brown sludge. If you see droopy, curly cannabis leaves, especially with young plants, look to the roots for answers.

CAUSE: OVERFERTILISATION

A heavy-handed approach to nutrients is ill-advised. Excessive doses of nitrogen-rich vegetative growth base nutes can cause clawing in leaves. Sometimes, they will even canoe. Similarly, overdoing it with the phosphorus and potassium during flowering will cause curly cannabis leaves and scorch the tips. Chlorosis is a common symptom in both cases.

Dial in feeding. Easier said than done right? Wrong! Almost every brand of well-known cannabis fertiliser offers a feeding chart free to download from their respective websites. Granted, not all cannabis varieties will respond in the same way to fertilisers.

It’s better to start low and go slow. You can incrementally increase doses without seeing leaves curling or clawing. But if you dive right in at maximum strength, you can expect plenty of curly cannabis leaves that will probably die and eventually drop-off.
It should go without saying, but we’ll say it again for good measure; make sure the nutrient solution is the right pH. That’s about 6.0pH for soil and a more precise 5.8pH for coco/hydroponics.

CAUSE: TEMPERATURES ARE TOO HOT

Heat stress can occur indoors or outdoors. If you see curling and nasty-looking brown fringing, your cannabis leaves are sending you a distress signal. Cannabis plants can photosynthesise efficiently at moderate temperatures up to 28°C. Anything above 30°C and your plants are in the danger zone. Combine this with low RH and you’ve got real problems. New leaves will grow gnarly and old leaves will curl yellow and maybe even burn to a rusty, brown crisp.

Indoor growers must constantly maintain the optimal environmental conditions. This starts with optimal light distance. The only way to keep the plant canopy in the sweet spot is to measure and adjust until mature plants peak in height during mid-late bloom, depending on the strain. Moreover, indoor growers can utilise air-con and fans to keep the grow-op cool.

Outdoor growers confronted with heat waves and drought conditions have less control than the indoor grower. Constructing a simple screen shade will keep plants slightly cooler and may prevent leaves from fraying and curling further. You can’t really revive scorched leaves and will have to remove older foliage beyond saving. Also, planting in white pots instead of black pots will keep the root zone cooler.

CAUSE: TEMPERATURES ARE TOO COLD

Cold temperatures can cause curly cannabis leaves too. Eventually, all kinds of leaf discolouration will develop. Sure, cooler nighttime temps late in bloom can add a dash of purple charm to buds, but prolonged exposure to temperatures below 10°C will kill your plants. Flowers will be loose and leafy if plants even make it to harvest. Coupled with high RH, buds will be moist and become vulnerable to Botrytis, AKA bud rot.

Indoors, if temps are too low, you can always add more grow lights and turn a negative into a positive. Outdoor growers might consider an early harvest, or if possible, moving plants indoors at night. Cannabis is a hardy plant species, but outside of the optimal 20–28°C temperature range, leaves will curl or claw.

A FINAL WORD ON CURLY CANNABIS LEAVES: GENETICS

Genetics are the cause of all kinds of cannabis leaf deformities and mutations. Some strains occasionally have a tendency towards curly leaves or other odd traits. Most growers will thin out these plants. All the shrewd cultivator can do is write it off as bad luck.

Sativa strains and many autoflowering varieties are sensitive to high doses of fertilisers. This is a trait that can cause problems for beginner growers. The solution is to research your reefer. Always find out as much as you can about the genetics of a strain before you decide to grow it. Curly cannabis leaves can be completely avoided if you know how to keep your plants healthy.

Cannabis leaves curling or clawing are signs your plants are suffering. Something is going wrong in the garden. This blog will help you save the stash.

Leaves cupping/canoeing up

Active Member

My oscillating fan broke 6 days ago (only managed to replace it yesterday) and about 2 days later I noticed the leaves started cupping only on my White Rhinos from GH. My Early Widow and the plants I started from bagseeds are looking fine.

I’m using a 600W HPS which is about 2ft from the top of the plants.
I have an oscillating fan on low blowing air at the plants which are now 26 days old and still vegging. They’re still growing albeit slowly.

These pics are 3 days old but they’re looking about the same with some of the leaves’ tips turning brown. The lower branches are still getting bigger though.

Now this is my Early Widow:

And the plants I started from bagseeds:

Their leaves seem to be starting to cup a bit too in those pics but they’re looking better now and it was really slight anyway.

Do you think the cupping is really caused by heat stress?
I’m really clueless right now, I really don’t want to lose my plants

jesus of Cannabis
Active Member

I don’t think that’s the problem, I’m not sure on how big the pots are but I’d say 5 liters or something along those lines.
I’m thinking about switching the light cycle to 12/12 in 2-3 days once I buy clonex so I can take a couple of cuttings but I’m hesitant because of how the leaves are looking.
On one of the plants the top leaves’ edges are really starting to look brown and burnt and the other plants are looking about as bad as the one in those pics :/

Oh and the affected leaves have an uneven color and feel kinda crispy.

dannlad
Active Member
Active Member
Active Member
bigv1976
Well-Known Member
DrFever
New Member

transplant them, and dont even think of cloning them yet there way to young might kill em if you do
as well raise your light up about a foot or so, when you water do you water the leafs if so stop just water soil STAY AWAY FROM LEAFS

TRY doin a flush on one plant as well lower your ph to 6.2

bigv1976
Well-Known Member

transplant them, and dont even think of cloning them yet there way to young might kill em if you do
as well raise your light up about a foot or so, when you water do you water the leafs if so stop just water soil STAY AWAY FROM LEAFS

TRY doin a flush on one plant as well lower your ph to 6.2

DrFever
New Member

well beats sitting there letting them wither away i tranplanted many plants in all stages of growth an never had them stressed out got larger pot added soil wetted it and then cut the other pot then put complete soil and plant on top of soil added all round watered and worked out great

dude i just transplanted 2 nights ago from FFOF to MG organic and the plant is acting like its alive and awake now. almost thanking me haha look at your quote lol

Active Member

Thanks for the help guys, +rep

I’m pretty sure it’s not under watering, I’ve been watering every 2-3 days when the soil starts feeling dry a couple of inches below the surface. Also, I water the soil, not the plants themselves.
I just raised my light about half a foot and put the fan on medium instead of low.

I’ll borrow my friend’s pH meter tomorrow and post the water and runoff pH.

Anything else I should do?

bigv1976
Well-Known Member

well beats sitting there letting them wither away i tranplanted many plants in all stages of growth an never had them stressed out got larger pot added soil wetted it and then cut the other pot then put complete soil and plant on top of soil added all round watered and worked out great

dude i just transplanted 2 nights ago from FFOF to MG organic and the plant is acting like its alive and awake now. almost thanking me haha look at your quote lol

Serapis
Well-Known Member

transplant them, and dont even think of cloning them yet there way to young might kill em if you do
as well raise your light up about a foot or so, when you water do you water the leafs if so stop just water soil STAY AWAY FROM LEAFS

TRY doin a flush on one plant as well lower your ph to 6.2

Taking cuttings will not kill a plant, however transplanting a plant that is obviously under stress is not a bright idea. Your advice about watering or wetting leaves is off as well, as the plant isn’t showing ANY signs of spot burns. Foliar feeding is beneficial, however, where does the OP even mention that he does this? Your advice is all over the place, yet fails to address the plant’s symptoms.

The only time a leaf will cup like that is for one of two reasons only, one is heat stress, lack of water. The other is a Mg deficiency which is caused by a PH below 6.4 in soil (in my opinion, DrFever’s sugested 6.2 is closer to a hydro PH than it is soil), or from using RO water for feeding and watering, or from using tap water with chlorine in it, in which case you want to add some Cal-Mag if using liquid ferts, or Epsom salts if you are growing organically.

You stated in your OP that the 600 watt is 2 feet above the plant tops. Don’t raise it any further as suggested by the Fever, as you’ll only be dissipating additional light. 2′ is plenty high enough for a 600w. I prefer 12″, but I’m air cooled. If you need to raise the light higher than 2′, better take a look at your ventillation and heat build up issues.

My oscillating fan broke 6 days ago (only managed to replace it yesterday) and about 2 days later I noticed the leaves started cupping only on my White…